This invention generally relates to a toric lens finer-polisher. More specifically, this invention relates to a novel apparatus for the fining and/or polishing of ophthalmic toric lenses.
In ophthalmic optics, lens blanks are formed from glass or plastic, and a convex or concave surface of the lens is I5 mounted upon a retaining member known as a lens block. The lens and block are then accurately mounted upon a grinding apparatus wherein a toroidal surface of compound prescriptive value is "rough ground" into a concave portion of the lens. In this regard, a first principal meridian of the lens typically has a different dimension with respect to a second principal meridian normal to the first. Following the initial grinding operation, an ophthalmic lens is fined and then polished to a final prescriptive value. Left and right lenses are then mounted upon an edge grinding machine to cut the outer peripheral shape required for compatability with an eyeglass frame of an ultimate user or wearer.
The basic concept governing implementation of a machine which finishes lenses provides a means of holding a toric tool and a lens to be finished in intimate contact. The tool and lens are driven such that relative motion between the lens and the tool furnishes a degree of abrasion required for fining and polishing the lens. For those skilled in the art, it is understood that the ancillary materials of coolants, abrasives and polishes are necessary for the process and will not be discussed herein.
An early device in the lens finishing industry included cylindrical lens finishers in which the toric surface of a lapping tool was held in engagement with the lens surface and moved relative thereto in a path referred to as a "break-up" motion. Such break-up movement prevents ridges, grooves and other aberrations from being formed in the lens surface, such ridges, grooves and aberrations occurring when regular or uniform motion is utilized. In addition to orbital, break-up motion of the lapping tool, the aforementioned device discloses movement of the lens in a transverse motion from side to side.
Although finer-polisher systems of the type previously described were widely utilized, room for significant improvement remained. For example, systems such as that disclosed suffered from relatively lower speed of motion between the lapping tool and the lens, and any attempt to increase the relative speed of motion between the lapping tool and the lens caused a sacrifice in the lens finishing ability of the system. It was also considered desirable to be able to easily vary the amplitude of the orbital, break-up motion of such a system.
In order to overcome disadvantages of the previously described system, a finer/polisher machine was developed in which first and second assemblies were provided for carrying a lapping tool and a lens, respectively, and for imparting an orbital break-up motion during the fining and polishing operation. The amplitude of orbital movement in this I0 arrangement was variable by application of a cam assembly for adjustment of the degree of orbital break-up motion of the lens mounting and/or lapping tool. However, there was also a disadvantage with this system in that it was not possible to decrease the speed and amplitude of motion of a lens lapping tool for enhanced control, while at the same time maintaining a high degree of relative motion between a lens and the tool to facilitate rapid fining and polishing. It was also considered desirable to have a system for achieving motion in an X-Y plane which would eliminate any tendency for the creation of a sawtooth aberration on the lens. Elimination of these problems was thought to be desirable because the rate of finishing of an ophthalmic lens could be increased without sacrificing lens finishing quality of the system.
Accordingly, a further finer-polisher device was developed in which a frame and gimbal-mounted assembly for providing an orbital break-up motion to a lens lapping tool, in combination with an X-Y motion assembly connected to the frame and lens, provided a smooth, Lissajous figure movement to the lens. In the X-Y motion assembly, commonly driven first and second cams provide movement in the X and Y directions, respectively.
In general, in break-up motion devices used with cylindrical lens surfaces, the base and cross-curve of the lapping tool must be maintained in parallel relationship with respect to the base and cross-curve of the lens. The finer-polisher machines previously mentioned employed a gimbal assembly mounted between a pair of brackets extending outwardly from a sidewall of the machine. The gimbal assembly was located a relatively short distance, as measured along a tool shaft, from the top of the lapping tool. The gimbal prevents rotation of the tool shaft about its own longitudinal axis. This is important because the cylindrical surface of the lapping tool must be maintained in accurate rotational alignment with the surface of the lens to be finished.
The relatively short length of the tool shaft from the gimbal to the tool holder, however, has posed problems. For example, lens hydroplaning and excessively long strokes of the tool have resulted. More specifically, certain portions of the lens surface will not polish; typically, these areas or zones are obliquely disposed from the cylindrical axis of the lens, and are referred to as "grey" areas.
As a result of the deficiencies previously mentioned, complex break-up motions have been required, especially in order to cope with some of the idiosyncrasies of the machines. More and more complex break-up motions have tended to reduce some of the problems. However, such complex motions have had the disadvantage of adversely influencing the integrity of the lens surface radii, which in turn has degraded optical integrity. In some cases, rubber supports have been used in order to compensate for this problem by allowing the tool to move or rotate off-axis. However, this has created a serious flaw in axis integrity which, in some cases, has followed an "S" path instead of a straight line, as desired.
An improved device addressed the problems previously encountered due to a relatively short tool shaft length from the gimbal to the tool holder, relative to the orbit of the shaft, by suggesting use of a longer tool shaft. By using a longer tool shaft, the tendency to skew with tool excursion in an oblique direction was minimized.
While the general observation that a relatively longer tool shaft enhances the finer-polisher operation is significant, room for worthwhile improvement remains regarding optimization of operation. In this regard it would be desirable to specifically describe an optimal shaft length such that the finer-polisher configuration produces a minimum disparity between the tool and lens axes that may be tolerated to yield high quality optical surfaces in a relatively short amount of time.
The difficulties and desire for further improvement suggested in the preceeding are not intended to be exhaustive but rather are among many which may tend to reduce the effectiveness of prior lens finer-polisher devices. Other noteworthy concerns may also exist; however, those presented above should be sufficient to demonstrate that toric lens finer-polishers appearing in the past will admit to worthwhile improvement.